How to Change a Cummins 12 Valve Thermostat

Dodge and other vehicle companies have used Cummins 12 valve engines through at least 1996. A thermostat is an essential part of the cooling system in gasoline and diesel engines. A bad thermostat needs to be replaced immediately to prevent damage to the engine. This article will tell you how to change a Cummins 12 valve thermostat.

Steps

1. 1
   Disconnect the negative (black) cable from the engine's battery.

   
   
2. 2
   Drain the engine's coolant into a container. Close the container as soon as liquid stops draining from the truck.
3. 3
   Lift the belt tensioner with a 3/8-inch (9.53 mm) breaker bar and remove the drive belt.
4. 4
   Disconnect the engine's upper radiator hose from the thermostat's cover. Place the hose to the side so it doesn't cover the alternator.
5. 5
   Loosen the alternator's mounting bolts and lower the alternator so it is no longer blocking access to the thermostat.
6. 6
   Unfasten the thermostat's housing. Take out the engine lifting bracket, followed by the thermostat with its seal.
7. 7
   Mount the new thermostat to its cover. Ensure that the tong on the thermostat is lined up with the slot of the housing.
   • Having proper alignment allows air to pass through the jiggle pins and through the radiator neck.
8. 8
   Remount the engine lifting bracket, new thermostat and seal. Check that the seal is installed with the beveled side facing outward.
9. 9
   Place the thermostat housing in the correct position in the engine and use a torque wrench to tighten the bolts to 18 foot pounds (24 Nm). Reconnect the upper radiator hose to the thermostat cover.
10. 10
    Place the alternator back into its correct position. Tighten the upper bolt to 18 foot pounds (24 Nm) and the lower bolt to 32 foot pounds (43 Nm).
11. 11
    Replace the drive belt and reconnect the negative battery cable. Run your engine until the thermostat opens.
12. 12
    Fill the radiator with coolant and check for leaks. If any leaks are found, turn off your diesel engine and check bolts and hoses for secure fits.
13. 13
    Turn off the engine and let the vehicle cool. Recheck coolant levels. Add more antifreeze with the thermostat plug removed until it overflows the plug hole.
14. 14
    Put the thermostat plug back into place and top off the radiator.

    
    

Warnings

• Antifreeze is toxic to humans and animals. It is important to close containers and clean up any spills, since its sweet smell and taste attracts children, pets and wildlife.

Things You'll Need

• Sealable container
• 3/8-inch (9.53mm) breaker bar
• Torque wrench set with sockets
• Antifreeze

Sources and Citations

• Article provided by wikihow the wikihow manual. Please edit this article and find author credits at the original wikiHow article on How to Change a Cummins 12 Valve Thermostat All content on wikiHow can be shared under a Creative Commons license.